Apparatus for modifying the configuration of an exposed surface of a viscous fluid

ABSTRACT

A method and apparatus for achieving a level exposed surface of a viscous material pool for applying viscous material to at least one semiconductor component by contacting at least a portion of the semiconductor component with viscous material within a reservoir. A level viscous material exposed surface is achieved by using at least one mechanism in association with the reservoir. The mechanism is configured to level the exposed surface of viscous material and maintain the exposed surface at a substantially constant level. The reservoir may be shaped such that the exposed surface of viscous material is supplied to a precise location.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of application Ser. No.09/944,233, filed Aug. 30, 2001, pending, which is a continuation ofapplication Ser. No. 08/906,578, filed Aug. 5, 1997, now U.S. Pat. No.6,336,973.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to achieving a level surface on anexposed surface of a viscous fluid. More particularly, the presentinvention relates to maintaining a level surface on a pool of adhesivematerial for applying the adhesive material to the lead fingers bycontacting the lead fingers with the pool of adhesive material.

[0004] 2. State of the Art

[0005] Higher performance, lower cost, increased miniaturization ofsemiconductor components, and greater packaging density of integratedcircuits are goals of the computer industry. One way to reduce theoverall cost of a semiconductor component is to reduce the manufacturingcost of that component. Lower manufacturing costs can be achievedthrough faster production and/or reduction in the amount of materialsused in fabricating the semiconductor component.

[0006] One area where faster production and reduction in material usagecan be achieved is in the area of lead frame attachment to semiconductordice. U.S. Pat. No. 5,286,679 issued Feb. 15, 1994 to Farnworth et al.(“the '679 patent”), assigned to the assignee of the present inventionand hereby incorporated herein by reference, teaches attaching leads toa semiconductor device with adhesive material in a “lead-over-chip”(“LOC”) configuration. The '679 patent teaches applying a patternedthermoplastic or thermoset adhesive layer to a semiconductor wafer. Theadhesive layer is patterned to keep the “streets” on the semiconductorwafer clear of adhesive for saw cutting and to keep the wire bondingpads on the individual dice clear of adhesive for wire bonding.Patterning of the adhesive layer is generally accomplished by hot orcold screen/stencil printing or dispensing by roll-on. Following theprinting and baking of the adhesive layer on the semiconductor wafer,the individual dice are singulated from the semiconductor wafer. Duringpackaging, each adhesive coated die is attached to lead fingers of alead frame by heating the adhesive layer and pressing the lead fingersonto the adhesive. If the adhesive layer is formed of a thermosetmaterial, a separate oven cure is required. Furthermore, the adhesivelayer may be formulated to function as an additionalpassivating/insulating layer or alpha barrier for protecting thepackaged die.

[0007] Although the teaching of the '679 patent is an effective methodfor attaching leads in a LOC configuration, it is difficult to achievean adequate profile on the adhesive such that there is sufficient areaon the top of the adhesive to attach the lead fingers. The processdisclosed in the '679 patent is illustrated in FIGS. 23-29. FIG. 23illustrates a side, cross-sectional view of a semiconductor substrate302 with a bond pad 304, wherein a stencil or a screen print template306 has been placed over the semiconductor substrate 302, generally asilicon wafer. The stencil or screen print template 306 is patterned toclear the area around the bond pads 304 and to clear street areas 308for saw cutting (i.e., for singulating the substrate into individualdice). An adhesive material 310 is applied to the stencil or screenprint template 306, as shown in FIG. 24. Ideally, when the stencil orscreen print template 306 is removed, adhesive prints 312 are formedwith vertical sidewalls 314 and a planar upper surface 316, as shown inFIG. 25. However, since the adhesive material 310 must have sufficientlylow viscosity to flow and fill the stencil or screen print template 306,as well as allow for the removal of the stencil or screen print template306 without the adhesive material 310 sticking thereto, the adhesivematerial 310 of the adhesive prints 312 will spread, sag, or flowlaterally under the force of gravity after the removal of the stencil orscreen print template 306, as shown in FIG. 26. This post-applicationflow of adhesive material 310 can potentially cover all or a portion ofthe bond pads 304 or interfere with the singulating of the semiconductorwafer by flowing into the street areas 308.

[0008] Furthermore, and of even greater potential consequence than bondpad or street interference is the effect that the lateral flow or spreadof adhesive material 310 has on the adhesive material upper surface 316.As shown in FIG. 27, the adhesive material upper surface 316 is thecontact area for lead fingers 318 of a lead frame 320. Thegravity-induced flow of the adhesive material 310 causes the oncerelatively well defined edges 322 of the adhesive material to curve,resulting in a loss of surface area 324 (ideal shape shown in shadow)for the lead fingers 318 to attach to. This loss of surface area 324 isparticularly problematical for the adhesive material upper surface 316at the longitudinal ends 326 thereof. At the adhesive materiallongitudinal ends 326, the adhesive material flows in three directions(to both sides as well as longitudinally), causing a severe curvature328, as shown in FIGS. 28 and 29. The longitudinal ends of the adhesiveprint on patch flow in a 180° flow front, resulting in blurring of theprint boundaries into a curved perimeter. This curvature 328 results incomplete or near complete loss of effective surface area on the adhesivematerial upper surface 316 for adhering the outermost lead fingerclosest to the adhesive material longitudinal end 326 (lead finger 330).This results in what is known as a “dangling lead. Since the lead finger330 is not adequately attached to the adhesive material longitudinal end326, the lead finger 330 will move or bounce when a wirebondingapparatus (not shown) attempts to attach a bond wire (not shown) betweenthe lead finger 330 and its respective bond pad 304 (shown from the sidein FIG. 29). This movement can cause inadequate bonding or non-bondingbetween the bond wire and the lead finger 330, resulting in the failureof the component due to a defective electrical connection.

[0009] LOC attachment can also be achieved by attaching adhesive tape,preferably insulative, to an active surface of a semiconductor die, thenattaching lead fingers to the insulative tape. As shown in FIG. 30, twostrips of adhesive tape 410 and 410′ are attached to an active surface412 of a semiconductor die 404. The two adhesive tape strips 410, 410′run parallel to and on opposing sides of a row of bond pads 406. Leadfingers 402, 402′ are then attached to the two adhesive tape strips 410,410′, respectively. The lead fingers 402, 402′ are then electricallyattached to the bond pads 406 with bond wires 408. Although this methodis effective in attaching the lead fingers 402, 402′ to thesemiconductor die 404, this method is less cost effective than usingadhesive since the cost of adhesive tape is higher than the cost ofadhesive material. The higher cost of the adhesive tape is a result ofthe manufacturing and placement step which are required with adhesivetapes. The individual tape segments are generally cut from a larger tapesheet. This cutting requires precision punches with extremely sharp andaccurate edges. These precision punches are expensive and they wear outover time. Furthermore, there is always waste between the segments whichare punched out, resulting in high scrap cost. Moreover, once punch outis complete, the tape segments are placed on a carrier film fortransport to the die-attach site. Thus, there are problems withplacement, alignment, and attachment with film carriers, plus the costof the film carrier itself. LOC attachment can further be achieved byplacing adhesive material on the lead fingers of the lead frame ratherthan on the semiconductor substrate. As shown in FIG. 31, the adhesivematerial 502 may be spray applied on an attachment surface 504 of leadfingers 506. However, the viscous nature of the adhesive material 502results in the adhesive material 502 flowing down the sides 508 of thelead finger 506 and collecting on the reverse, bond wire surface 510 ofthe lead finger 506, as shown in FIG. 32. The adhesive material 502which collects and cures on the bond wire surface 510 interferes withsubsequent wirebonding which, in turn, can result in a failure of thesemiconductor component. The flow of adhesive material 502 for theattachment surface 504 to the bond wire surface 510 can be exacerbatedif the lead fingers 506 are formed by a stamping process rather than byetching, the other widely employed alternative. The stamping processleaves a slight curvature 512 to edges 514 of at least one surface ofthe lead finger 506, as shown in FIG. 33. If an edge curvature 512 isproximate the lead finger attachment surface 504, the edge curvature 512results in less resistance (i.e., less surface tension) to the flow ofthe adhesive material 502. This, of course, results in the potential fora greater amount of adhesive material 502 to flow to the bond wiresurface 510.

[0010] Furthermore, present methods of adhesive material application ona surface (whether of the semiconductor die or the lead fingers) tend towaste adhesive material. For example, spray application loses a greatdeal of adhesive material because not all of the sprayed adhesivematerial attaches to the target surface. As another example, thepatterning of an adhesive layer on a semiconductor die, such asdescribed in the '679 patent, results in a substantial area of theadhesive pattern not being utilized to attach leads.

[0011] Thus, it can be appreciated that it would be advantageous todevelop a method and apparatus for rapidly applying an adhesive materialto a lead finger with little waste of adhesive material.

BRIEF SUMMARY OF THE INVENTION

[0012] The present invention relates to a method for applying anadhesive material to lead fingers of a lead frame wherein surfaces ofthe lead fingers which receive the adhesive material face downward tocontact a pool of adhesive material. Preferably, the adhesive materialcures with the lead frame in this downward facing position. Theadvantages of placing viscous material, such as an adhesive material, ina downward facing position is described in U.S. patent application Ser.No. 08/709,182 by Tongbi Jiang and Syed S. Ahmad filed Sep. 6, 1996,assigned to the assignee of the present invention and herebyincorporated herein by reference. An adhesive reservoir retaining theadhesive material can be shaped such that the exposed surface (pool) ofthe adhesive material is in a precise location. When the lead fingerscontact the exposed surface of the adhesive material, the adhesivematerial attaches to only specific, desired portions of the leadfingers.

[0013] Rather than gravitational forces causing the adhesive material toflow and expand as when on top of the lead frame, the gravitationalforces on the inverted lead frame maintain the shape and boundarydefinition of the adhesive material. It is, of course, understood thatthe viscous adhesive material must be compatible with the lead fingermaterial so as to adhere thereto and must not be of such a low viscositythat it drips when the lead fingers are removed from contact with theadhesive material pool. Preferably, the viscous materials haveviscosities between about 1000 cps and 500,000 cps.

[0014] Of critical importance to the application of the adhesivematerial to the lead fingers in the method described above is thelevelness of the exposed surface of the adhesive material of the pool.If the exposed surface is not level, the lead fingers may extend toodeeply into the adhesive material. When this occurs, the adhesivematerial may wet sides of the lead finger and may even wet a bond wiresurface of the lead finger. If the adhesive material wets the bond wiresurface, the adhesive material may interfere with a wirebonding stepsubsequent to LOC attachment of the lead fingers to an active surface ofa semiconductor die.

[0015] A preferred method of controlling the levelness of the exposedsurface is by attaching a coating stencil having small apertures, suchas a screen or a plate with slots, to the adhesive reservoir, such thatthe only outlet for the adhesive material is through the apertures inthe coating stencil. The adhesive material is thus forced through thecoating stencil. The surface tension between walls of the smallapertures and the adhesive material flattens out the exposed surface ofthe adhesive material. This allows a larger area to be printed with amore uniform thickness layer than if the coating stencil is not used. Itis, of course, understood that the flatness or shape of the adhesivematerial can be controlled by the design of the apertures of the coatingstencil. Thus, the present invention is an efficient way to use thesurface tension of the adhesive material to control surface area andthickness of the adhesive material available for application to leadfingers.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0016] While the specification concludes with claims particularlypointing out and distinctly claiming that which is regarded as thepresent invention, the advantages of this invention can be more readilyascertained from the following description of the invention when read inconjunction with the accompanying drawings in which:

[0017]FIG. 1 is a top plan view of a typical lead frame ribbon;

[0018]FIGS. 2 and 3 are schematic representations of one process of thepresent invention;

[0019]FIG. 4 is a schematic representation of an alternate process ofthe present invention;

[0020] FIGS. 5-7 are side views of a process of contacting lead fingerswith an adhesive material according to a method of the presentinvention;

[0021]FIG. 8 is a side cross-sectional view of a lead finger afteradhesive material attachment according to a method of the presentinvention;

[0022]FIG. 9 is a cross-sectional view of a lead finger along line 9-9of FIG. 8 after adhesive material attachment;

[0023]FIG. 10 is a cross-sectional view of a lead finger after adhesivematerial attachment, wherein the adhesive material exhibits excessivewetting of the lead finger;

[0024]FIG. 11 is a schematic representation of a mechanical mechanismfor maintaining the height of an exposed surface of an adhesivematerial;

[0025]FIG. 12 is a schematic representation of a height detection andcontrol loop for maintaining the height of an exposed surface of anadhesive material;

[0026]FIG. 13 is a plan view of a coating stencil of the presentinvention;

[0027]FIG. 14 is a plan view of an alternate coating stencil of thepresent invention;

[0028]FIG. 15 is a side cross-sectional view of an adhesive reservoir ofthe present invention;

[0029]FIG. 16 is a top plan view of the adhesive reservoir of thepresent invention shown in FIG. 15 along line 16-16;

[0030]FIG. 17 is a side plan view of stenciled and non-stenciledadhesive material profiles;

[0031]FIG. 18 is a side plan view of a stenciled adhesive materialprofile after the induction of a vacuum;

[0032] FIGS. 19-21 are side cross-sectional views of a technique offorming an adhesive film on lead fingers according to the presentinvention;

[0033]FIG. 22 is a schematic representation of another multiple adhesivematerial attachment process of the present invention;

[0034] FIGS. 23-29 are side cross-sectional views of a prior arttechnique of forming adhesive areas on a substrate for LOC attachment;

[0035]FIG. 30 is a top view of a prior art technique of LOC attachmentusing adhesive tape; and

[0036] FIGS. 31-33 are side cross-sectional views of a prior arttechnique of forming adhesive areas on lead fingers for LOC attachment.

DETAILED DESCRIPTION OF THE INVENTION

[0037]FIG. 1 illustrates a portion of an exemplary lead frame ribbon100. It should be understood that the figures presented in conjunctionwith this description are not meant to be actual views of any particularportion of an actual semiconductor device or component, but are merelyidealized representations which are employed to more clearly and fullydepict the process of the invention than would otherwise be possible.Individual lead frames 102, each including a plurality of lead fingers104, are formed in a long, thin strip of conductive material 106, suchas copper, copper alloy, or the like. The lead frames 102 are generallyformed by a stamping process or an etching process. The lead frames 102are formed side-by-side along the conductive material strip 106 whereinthe conductive material strip 106 includes a plurality of indexing holes107, 107′ on opposing lengthwise edges 109, 109′, respectively, of theconductive material strip 106. The indexing holes 107, 107′ are used tomove the lead frame ribbon 100 and align the lead frames 102 throughouta process of attaching the lead frames 102 to semiconductor dice (notshown).

[0038]FIGS. 2 and 3 illustrate a schematic of one process of the presentinvention. Elements common to FIGS. 1, 2, and 3 retain the same numericdesignation. The lead frame ribbon 100, such as illustrated in FIG. 1,is fed from a source 108, such as a spool, to an adhesive reservoir 110.As shown in FIG. 3, the lead fingers 104 (not shown) of the lead frame102 (not shown) are aligned over the adhesive reservoir 110 and the leadframe ribbon 100 is biased downward in direction 112, such as byhydraulic, pneumatic, or electrically-powered biasing mechanisms 116, tocontact an adhesive material 114. The adhesive material 114 may be anyviscous adhesive material including but not limited to thermoplastics,thermoses resins, flowable pastes, and B-stage adhesive materials.Preferred adhesive materials 114 include cyanate ester, bismaleimide,epoxy, and polyimide.

[0039]FIG. 4 illustrates a schematic of another process of the presentinvention which is similar to the process of FIGS. 2 and 3. Elementscommon to FIGS. 2 and 3 and FIG. 4 retain the same numeric designation.The only difference between the processes of FIGS. 2 and 3 and FIG. 4 isthat the process of FIG. 4 employs an elevator mechanism 117 to move theadhesive reservoir 110 in an upward direction 120 to contact the leadfingers 104 rather than biasing the lead frame ribbon 100 downward tothe adhesive reservoir 110.

[0040] It is, of course, understood that the biasing and elevatormechanisms 116 and 117 shown in FIGS. 2 and 3 are not required to bringthe adhesive material 114 into contact with the lead fingers 104.Instead, the lead fingers 104 may be brought into close proximity to theadhesive reservoir 110 and additional adhesive material 114 may bedelivered by a pump to the adhesive reservoir 110 to raise the level ofthe adhesive material 114 to contact the lead fingers 104, or to providea moving wave or surge of adhesive material traveling across thereservoir 110.

[0041] FIGS. 5-7 illustrate side views of the lead fingers 104 beingbrought into contact with the adhesive material 114 and being retractedtherefrom. Elements common to FIGS. 2-4 and FIGS. 5-7 retain the samenumeric designation. As shown in FIG. 5, the lead fingers 104 arepositioned over the adhesive reservoir 110. The adhesive reservoir 110has the adhesive material 114 extending above edges 111 of the adhesivereservoir 110. Due to the forces of adhesion and surface tensioninherent in the adhesive material 114, an exposed surface 122 of theadhesive material 114 will form a meniscus, or convex-shapedconfiguration, above the reservoir edges 111.

[0042] As shown in FIG. 6, the lead fingers 104 are lowered onto orproximate the exposed surface 122 of the adhesive material 114. When abottom surface 124 of the lead fingers 104 comes in contact with theexposed surface 122 of the adhesive material 114, the adhesive material114 wets out across the bottom surface 124 of the lead finger 104. Asshown in FIG. 7, when the lead fingers 104 are retracted from theadhesive material 114, the cohesion of the adhesive material 114 withthe lead fingers 104 pulls some of the adhesive material 114 from thebulk of the adhesive material 114 to form an adhesive film 126 on thebottom surface 124 of the lead finger 104. The thickness of the adhesivefilm 126 can range from 0.1 to 15 mils, depending on the viscosity ofthe adhesive material 114. Changing the shape of the lead finger 104,changing the rheology of the adhesive material 114, pre-coating the leadfinger 104 with a surfactant, such as AMP, or placing a solvent in theadhesive material 114 to improve wetting, and/or adding adhesionpromoters, such as silane, siloxane, or polyimide siloxane, to theadhesive material 114 will also change the thickness and/or pattern ofthe adhesive film 126. It is, of course, understood that the adhesivematerial 114 must be capable of adhering to the lead fingers 104 andmust not be of such a low viscosity that it drips when the lead fingers104 are removed from contact with the exposed surface 122 of theadhesive material 114.

[0043]FIG. 8 is a side cross-sectional view of a lead finger 104 afteradhesive material 114 application. FIG. 9 is a cross-sectional view ofthe lead finger 104 of FIG. 8 along line 9-9. As shown in FIGS. 8 and 9,by only contacting the bottom surface 124 of the lead finger 104 withthe exposed surface 122 of the adhesive material 114, the adhesivematerial 114 will not wet sides 128 of the lead finger 104 and, ofcourse, will not collect on a bond wire surface 130 of a lead finger 104(the bond wire surface 130 is the lead finger surface where a bond wireis subsequently attached during further processing). Since the adhesivematerial 114 does not collect on the bond wire surface 130, there willbe no adhesive material 114 to interfere with a subsequent wirebondingstep subsequent to LOC attachment of the lead fingers 104 to an activesurface of a semiconductor die.

[0044] Referring back to FIG. 5, the adhesive reservoir 110 can beshaped such that the exposed surface 122 of the adhesive material 114 isin a precise location. When the lead fingers 104 contact the exposedsurface 122 of the adhesive material 114, the adhesive material 114attaches to only specific, desired portions of the lead fingers 104.

[0045] It is very important that the exposed surface 122 be as level aspossible. If the exposed surface 122 is not level, the lead fingers 104may extend too deeply into the adhesive material 114. When this occurs,the adhesive material 114 may wet the lead finger sides 128 and may evenwet the lead finger bond wire surface 130, as shown in FIG. 10. If theadhesive material 114 wets the bond wire surface 130, the adhesivematerial 114 may interfere with a wirebonding step subsequent to LOCattachment of the lead fingers 104 to an active surface of asemiconductor die, as mentioned above.

[0046] Numerous techniques may be used to keep the exposed surface 122of the adhesive material 114 level. It is, of course, understood thatexposed surface 122 extends from the adhesive reservoir 110 due to aslight excess of adhesive material 114 within the adhesive reservoir110. As shown in FIG. 11, the adhesive material 114 is pumped to theadhesive reservoir 110 from an adhesive material source (not shown) by apump 132. A desired exposed surface height 134 of exposed surface 122can be achieved by feeding an excess of adhesive material 114 into theadhesive reservoir 110 such that an initial exposed surface height 136is higher than the desired exposed surface height 134. A meteringmechanism, such as wiper 138, can be utilized to meter the adhesivematerial 114 from the initial exposed surface height 136 to the desiredexposed surface height 134.

[0047] Moreover, a desired exposed surface height 134 of exposed surface122 can be achieved by feeding an excess of adhesive material 114 intothe adhesive reservoir 110 such that an initial exposed surface height136 is higher than the desired exposed surface height 134. The adhesivematerial 114 is then drawn back (e.g., by vacuum), which results in aflattening of the exposed surface 122.

[0048] Furthermore, a variety of feed back and feed forward controlschemes may be used to control the desired exposed surface height 134 ofthe exposed surface 122. One such control scheme is shown in FIG. 12.Elements common to FIG. 11 and FIG. 12 retain the same numericdesignations. A height detection mechanism, shown as a light (preferablya laser) transmitter 140 and a light receiver 142, is used to determinethe height of the exposed surface 122. The control signal 144 fromcontrol system 200 triggers the pump 132 to stop or a valve (not shown)to shut when the desired exposed surface height 134 is achieved.

[0049] It is, of course, understood that precise control of the leadframe position relative to the exposed surface 122 is required toaccurately control the depth to which the lead fingers 104 are pressedinto the adhesive material 114.

[0050] A preferred method of controlling the levelness of the exposedsurface 122 is by forcing or extruding the adhesive material 114 througha coating stencil having small apertures, such as a screen or a platewith slots. Such a coating stencil 150 is shown in FIG. 13. The coatingstencil 150 is a flat plate 152 having a plurality of slots 154. Thecoating stencil 150 shown has twenty-three parallel slots 154approximately 0.260 inches in length 158 and approximately 0.010 inchesin width 160, with the slots 154 being on parallel centerline pitch 162of approximately 0.020 inch from one another. An alternate coatingstencil 156 is shown in FIG. 14. The coating stencil 156 is a screencomprising a flat plate 157 having a plurality of square or rectangularapertures 159. It is, of course, understood that the apertures may be ofany size (depending on the viscosity of the adhesive material) and anyshape, including triangles, rectangles, squares, circles, ovals, or thelike.

[0051] The coating stencil 150 is attached to an adhesive reservoir 180.The exemplary adhesive reservoir 180, shown in FIGS. 15 and 16 withoutthe coating stencil attached, comprises a housing 164 having an adhesiveinflow chamber 166 in fluid communication with a pool chamber 168. Thecoating stencil 150 is attached proximate an upper surface 170 of thepool chamber 168, such that the only upward outlet for the adhesivematerial is through the apertures in the coating stencil. It is, ofcourse, understood that the adhesive reservoir 180 may include anadhesive circulation mechanism to circulate the adhesive material tomaintain the uniformity thereof.

[0052] The cohesion between the aperture (slot) walls (not shown) andthe adhesive material 114 flattens out the exposed surface 122 of theadhesive material 114. This allows a larger area to be printed with amore uniform thickness of the adhesive material 114 than if the coatingstencil 150 is not used. Put another way, the cohesion between theaperture walls and the adhesive material 114 basically pulls theadhesive material 114 down to the screen surface, which counteracts theforce caused by the surface tension of the adhesive material 114. As aresult, the adhesive material 114 is pulled to the coating stencil 150,thus flattening out. The mathematical formulation for the phenomena isΔp=2γ/R where Δp is the difference between the pressure within theadhesive material and the ambient air, γ is the surface tension of theadhesive material, and R is the radius of curvature when the adhesivematerial is extruded through the apertures in the coating stencil. Rwill be about the same for all openings, since Δp and γ are generallyconstant for most operations. Since the apertures are small, theextruded material is “flat” with about the same R.

EXAMPLE 1

[0053] An example of the difference between a non-stenciled adhesivematerial exposed surface 172 and stenciled adhesive material exposedsurface 174 is shown in FIG. 17. For this example, the adhesive material114 was Ablestik XR-041395-9™ Polyimide LOC Adhesive (AblestikLaboratories, Rancho Dominguez, Calif.) and the coating stencil 150 wasas described above for FIG. 13. Ablestik XR-041395-9™ has a viscosity of62,000 cps at 25° C. and a thixotropic index of 3.5. It is, of course,understood that the width, length, pitch and shape of the apertures inthe coating stencil will vary for different viscosities of adhesivematerials. A rule of thumb for determination of aperture size is that,for every viscosity increase of 25%, the aperture size should decreaseby 50%.

[0054] The illustration in FIG. 17 is an AutoCad™ program rendering of adigitized measurement of the non-stenciled adhesive material exposedsurface 172 and stenciled adhesive material exposed surface 174. Themaximum height 176 of the non-stenciled adhesive material exposedsurface 172 was approximately 0.07 inches above an upper surface 175 ofthe coating stencil 150 and the effective adhesion surface 178 of thenon-stenciled adhesive material exposed surface 172 was approximately0.26 inches wide. The maximum height 181 of the stenciled adhesivematerial exposed surface 174 was approximately 0.05 inches and theeffective adhesion surface 182 of the stenciled adhesive materialexposed surface 174 was approximately 0.33 inches wide. Thus, the use ofa coating stencil 150 resulted in an increase of effective adhesionsurface of about 21.2%. The effective adhesion surfaces 178, 182 aredetermined as the area from the maximum height 176, 181 of the stenciledadhesive material exposed surface 172, 174, to a position about 5 milsbelow the maximum height 176, 181.

[0055] It has also been found that an even more uniform profile for theexposed surface can be achieved by inducing a slight vacuum on a bottomside of the coating stencil 150 by any known technique. FIG. 18illustrates such a profile using the same adhesive material 114 andcoating stencil 150 described in FIG. 17, wherein a vacuum of betweenabout 2 and 3 inches of H₂O is applied. The vacuum method provided avery uniform coating at between about 0.02 and 0.03 inch in adhesivematerial height.

EXAMPLE 2

[0056] An example of one preferred embodiment of the coating process isillustrated in FIGS. 19-21. Elements common to FIGS. 19-21 and previousFIGs. retain the same designations. As shown in FIG. 19, the leadfingers 104 are brought into close proximity to the adhesive materialexposed surface 122. Sufficient adhesive material 114 is then deliveredto the adhesive reservoir 110 until the adhesive material exposedsurface 122 comes in contact with the bottom surface 124 of the leadfingers 104. At this point, additional adhesive material 114 isdelivered to the adhesive reservoir 110 to raise the adhesive materialexposed surface 122 about an additional 0.02 to 0.06 inches so that thelead fingers 104 are submerged past a top surface 184 of the adhesivematerial exposed surface 122, as shown in FIG. 20. The lead fingers 104remain in this position for a time sufficient to allow the adhesivematerial 114 to wet the bottom surface 124 of the lead fingers 104,preferably approximately 10 to 25 milliseconds. As shown in FIG. 21, theadhesive material exposed surface 122 is then lowered, thereby formingthe adhesive film 126 from the bulk of the adhesive material 114 on thebottom surface 124 of the lead finger 104. The lead frame ribbon 100 isthen indexed to the next site that requires coating. Before the adhesivematerial 114 is raised again, more adhesive material 114 is delivered,as required, to replenish the amount used in the previous coating cycle.

[0057] It is also understood that multiple reservoirs 110 could beconfigured as shown in FIG. 22. With such a configuration, the adhesivematerial 114 can be applied to the lead fingers 104 of multiple leadframes 102 simultaneously.

[0058] Once the adhesive material 114 has been applied to the leadfingers 104, the lead frame ribbon 100 may, optionally, be fed to acuring oven 118, shown in FIGS. 2, 3, 4, and 22, to set the adhesivematerial 114. A semiconductor die (not shown) then can be attached to alead frame 102 and adhesive film 126 by known LOC attach methods.

[0059] Having thus described in detail preferred embodiments of thepresent invention, it is to be understood that the invention defined bythe appended claims is not to be limited by particular details set forthin the above description as many apparent variations thereof arepossible without departing from the spirit or scope thereof.

What is claimed is:
 1. An apparatus for applying adhesive material toone or more underside surfaces of at least one semiconductor component,comprising: an adhesive reservoir configured to provide an exposedsurface of an adhesive material contained therein to each of one or moreunderside surfaces of at least one semiconductor component positionedthereover and to avoid contacting the exposed surface of adhesivematerial with a bond wire surface of each of the at least onesemiconductor components, the adhesive reservoir comprising at least onepool chamber for receiving the adhesive material and defined by at leastone upward facing opening, the adhesive reservoir shaped such that theexposed surface of adhesive material may be supplied to a preciselocation above the at least one upward facing opening, the adhesivematerial having a surface tension; and at least one mechanism associatedwith the adhesive reservoir, the at least one mechanism configured tolevel the exposed surface of adhesive material at the precise locationabove the at least one upward facing opening, to maintain the exposedsurface of adhesive material at a substantially constant height and tomanipulate the difference in pressure within the adhesive material andambient air to be equal to twice the surface tension of the adhesivematerial divided by a radius of curvature of the adhesive material. 2.The apparatus of claim 1, wherein the at least one upward facingopening, in combination with the surface tension of the adhesivematerial, is configured to provide an exposed surface comprising ameniscus.
 3. The apparatus of claim 1, wherein the at least onemechanism is configured to manipulate the surface tension of theadhesive material to flatten the exposed surface of the adhesivematerial.
 4. The apparatus of claim 1, wherein the at least onemechanism is configured to use the surface tension of the adhesivematerial to control surface area and thickness of the adhesive materialavailable for application to the at least one semiconductor component.5. The apparatus of claim 1, wherein the at least one mechanism furthercomprises at least one of a coating stencil, a pump and control system,a wiper, a vacuum, and a height detection mechanism.
 6. The apparatus ofclaim 1, wherein the at least one mechanism further comprises a coatingstencil including: a generally flat and generally horizontal topsurface; and a plurality of apertures aligned to wet the defined portionof the at least one semiconductor component with the adhesive material,the plurality of apertures sized and configured to control extrusion ofthe adhesive material through the coating stencil to define an area ofthe exposed surface of the adhesive material.
 7. The apparatus of claim6, wherein the coating stencil is disposed over the at least one upwardfacing opening of the at least one pool chamber, such that the onlyaccess from within the at least one pool chamber through the at leastone upward facing opening to above the adhesive reservoir is through theplurality of apertures of the coating stencil.
 8. The apparatus of claim6, wherein the plurality of apertures of the coating stencil issubstantially rectangular in shape.
 9. The apparatus of claim 6, whereinthe plurality of apertures of the coating stencil is substantiallysquare in shape.
 10. The apparatus of claim 6, wherein the plurality ofapertures of the coating stencil is positioned substantially parallel toeach other and is spaced so as to have a centerline pitch between eachaperture of the plurality of apertures of 0.020 inches (0.051 cm). 11.The apparatus of claim 10, wherein the plurality of apertures of thecoating stencil numbers 23 in quantity.
 12. The apparatus of claim 6,wherein the plurality of apertures of the coating stencil is 0.260 inch(0.660 cm) in length and is 0.010 inch (0.025 cm) in width.
 13. Theapparatus of claim 6, wherein the plurality of apertures of the coatingstencil is sized and configured as a result of considering adhesivematerial viscosity.
 14. The apparatus of claim 13, wherein the pluralityof apertures of the coating stencil is sized and configured to suit anadhesive material viscosity ranging from approximately 1000 to 500,000centipoise.
 15. The apparatus of claim 13, wherein the plurality ofapertures of the coating stencil is sized and configured to optimallyaccommodate an adhesive material viscosity of approximately 62,000centipoise.
 16. The apparatus of claim 13, wherein the plurality ofapertures of the coating stencil is sized and configured to optimallyaccommodate an adhesive material viscosity of approximately 62,000centipoise at a temperature of approximately 77° F. (25° C.).
 17. Theapparatus of claim 6, wherein the plurality of apertures of the coatingstencil is arranged generally parallel to each other and is spaced so asto have a centerline pitch between each aperture of the plurality ofapertures of 0.020 inches (0.051 cm).
 18. The apparatus of claim 17,wherein the plurality of apertures of the coating stencil numbers 23 inquantity.
 19. The apparatus of claim 17, wherein the plurality ofapertures of the coating stencil is 0.260 inches (0.660 cm) in lengthand is 0.010 inches (0.025 cm) in width.
 20. The apparatus of claim 6,further comprising a vacuum on a bottom side of the coating stencil. 21.The apparatus of claim 1, further comprising at least one secondmechanism configured to bring the defined portion of at least onesemiconductor component in contact with the exposed surface of adhesivematerial.
 22. The apparatus of claim 1, wherein the adhesive reservoirfurther comprises an adhesive circulation mechanism configured tocirculate the adhesive material and maintain uniformity of the adhesivematerial.
 23. The apparatus of claim 1, wherein the at least onemechanism further comprises a pump configured to supply the adhesivematerial to the adhesive reservoir and a control system to control thesupply of the adhesive material to the adhesive reservoir to controlextrusion of the adhesive material to a selectable height.
 24. Theapparatus of claim 1, wherein the at least one mechanism is attached tothe adhesive reservoir.
 25. The apparatus of claim 1, wherein the atleast one semiconductor component comprises at least one lead finger ona lead frame.
 26. An apparatus for applying viscous material to one ormore underside surfaces of at least one semiconductor component,comprising: a reservoir for providing an exposed surface of a viscousmaterial contained therein to only one or more underside surfaces of atleast a portion of at least one semiconductor component positionedthereover, the reservoir comprising at least one pool chamber in fluidcommunication with a viscous inflow chamber, the at least one poolchamber defined by at least one upward facing opening, the reservoirshaped such that the exposed surface of viscous material may be suppliedto a precise location above the at least one upward facing opening, theviscous material having a surface tension; at least one first mechanismconfigured to raise and lower the viscous material to a desiredselectable height above the at least one upward facing opening; and atleast one second mechanism associated with the reservoir, the at leastone second mechanism configured to level the exposed surface of viscousmaterial above the at least one upward facing opening, to maintain theexposed surface of viscous material at a substantially constant heightand to increase the effective exposed surface of viscous material. 27.The apparatus of claim 26, wherein the at least one first mechanismfurther comprises: a pump for supplying the viscous material to thereservoir; and a control system for controlling the supply of theviscous material to the reservoir.
 28. The apparatus of claim 26,wherein the exposed surface comprises a meniscus.
 29. The apparatus ofclaim 26, wherein the at least one second mechanism is configured tomanipulate the surface tension of the viscous material to flatten outthe exposed surface of the viscous material.
 30. The apparatus of claim26, wherein the at least one second mechanism is configured tomanipulate the difference in pressure within the viscous material andambient air to be equal to twice the surface tension of the viscousmaterial divided by a radius of curvature of the viscous material. 31.The apparatus of claim 26, wherein the at least one second mechanism isconfigured to use the surface tension of the viscous material to controlsurface area and thickness of the viscous material available forapplication to the at least one semiconductor component.
 32. Theapparatus of claim 26, wherein the at least one second mechanism furthercomprises at least one of a coating stencil, a wiper, a vacuum, and aheight detection mechanism.
 33. The apparatus of claim 26, wherein theat least one second mechanism further comprises at least one coatingstencil including: a generally planar horizontal top surface; and aplurality of openings positioned to wet the at least a portion of the atleast one semiconductor component with the viscous material, theplurality of openings sized and configured to control extrusion of theviscous material through the at least one coating stencil to furtherincrease the exposed surface of the viscous material.
 34. The apparatusof claim 33, wherein the at least one coating stencil is disposed overthe at least one upward facing opening of the at least one pool chamber,such that the only access from within the at least one pool chamberthrough the at least one upward facing opening to above the reservoir isthrough the plurality of openings of the at least one coating stencil.35. The apparatus of claim 33, wherein the plurality of openings of theat least one coating stencil is configured to apply the viscous materialto only a selected portion of the at least one semiconductor component.36. The apparatus of claim 33, wherein the plurality of openings of theat least one coating stencil is generally rectangular in shape.
 37. Theapparatus of claim 33, wherein the plurality of openings of the at leastone coating stencil is generally square in shape.
 38. The apparatus ofclaim 33, wherein the plurality of openings of the at least one coatingstencil is positioned generally parallel to each other and is spaced soas to have a centerline pitch between each opening of the plurality ofopenings of 0.020 inches (0.051 cm).
 39. The apparatus of claim 38,wherein the plurality of openings of the at least one coating stencilnumbers 23 in quantity.
 40. The apparatus of claim 33, wherein theplurality of openings of the at least one coating stencil is 0.260inches (0.660 cm) in length and is 0.010 inches (0.025 cm) in width. 41.The apparatus of claim 33, wherein the plurality of openings of the atleast one coating stencil is sized and configured as a result ofconsidering viscous material viscosity.
 42. The apparatus of claim 41,wherein the plurality of openings of the at least one coating stencil issized and configured to manage a viscous material viscosity ranging fromapproximately 1000 to 500,000 centipoise.
 43. The apparatus of claim 41,wherein the plurality of openings of the at least one coating stencil issized and configured to optimally accommodate a viscous materialviscosity of approximately 62,000 centipoise.
 44. The apparatus of claim41, wherein the plurality of openings of the at least one coatingstencil is sized and configured to optimally accommodate a viscousmaterial viscosity of approximately 62,000 centipoise at a temperatureof approximately 77° F. (25° C.).
 45. The apparatus of claim 33, whereinthe plurality of openings of the at least one coating stencil isarranged generally parallel to each other and is spaced so as to have acenterline pitch between each opening of the plurality of openings of0.020 inches (0.051 cm).
 46. The apparatus of claim 45, wherein theplurality of openings of the at least one coating stencil numbers 23 inquantity.
 47. The apparatus of claim 33, wherein the plurality ofopenings of the at least one coating stencil is 0.260 inches (0.660 cm)in length and is 0.010 inches (0.025 cm) in width.
 48. The apparatus ofclaim 33, wherein the at least one first mechanism further comprises avacuum on a bottom side of the at least one coating stencil.
 49. Theapparatus of claim 26, further comprising at least one third mechanismconfigured to bring the at least one semiconductor component in contactwith the exposed surface of viscous material.
 50. The apparatus of claim26, wherein the reservoir further comprises a circulation mechanismconfigured to circulate the viscous material and maintain uniformity ofthe viscous material.
 51. The apparatus of claim 26, wherein the atleast one second mechanism is attached to the reservoir.
 52. Theapparatus of claim 26, wherein the at least one semiconductor componentcomprises at least one lead finger of a lead frame.
 53. An apparatus forapplying adhesive material to one or more underside surfaces of at leastone semiconductor component, comprising: an adhesive reservoircomprising at least one upward facing opening and configured to providean exposed surface of an adhesive material contained therein to each ofone or more underside surfaces of at least one semiconductor componentpositioned thereover and to avoid contacting the exposed surface ofadhesive material with a bond wire surface of each of the at least onesemiconductor components, the adhesive material exhibiting a surfacetension; at least one first mechanism associated with the adhesivereservoir, the at least one first mechanism configured to raise andlower the adhesive material to a desired selectable height; and at leastone second mechanism associated with the adhesive reservoir, the atleast one second mechanism configured to level the exposed surface ofadhesive material at a precise location above the at least one upwardfacing opening.
 54. The apparatus of claim 53, wherein the at least oneupward facing opening in combination with the surface tension of theadhesive material is configured to provide the exposed surfacecomprising a meniscus.
 55. The apparatus of claim 53, wherein the atleast one second mechanism is configured to manipulate surface tensionof the adhesive material to flatten the exposed surface of the adhesivematerial.
 56. The apparatus of claim 53, wherein the at least one secondmechanism is configured to manipulate the difference in pressure withinthe adhesive material and ambient air to be equal to twice the surfacetension of the adhesive material divided by a radius of curvature of theadhesive material.
 57. The apparatus of claim 53, wherein the at leastone second mechanism is configured to use the surface tension of theadhesive material to control surface area and thickness of the adhesivematerial available for application to the at least one semiconductorcomponent.
 58. The apparatus of claim 53, wherein the at least onesecond mechanism further comprises at least one of a coating stencil, awiper, a vacuum, and a height detection mechanism.
 59. The apparatus ofclaim 53, wherein the at least one second mechanism further comprises atleast one coating stencil including: a generally planar horizontal topsurface; and a plurality of openings positioned to wet the one or moreunderside surfaces of the at least one semiconductor component with theadhesive material, the plurality of openings sized and configured tocontrol extrusion of the adhesive material through the at least onecoating stencil to further increase the exposed surface of the adhesivematerial.
 60. The apparatus of claim 59, wherein the at least onecoating stencil is disposed over the at least one upward facing opening,such that the only access from within the at least one upward facingopening to above the reservoir is through the plurality of openings ofthe at least one coating stencil.
 61. The apparatus of claim 59, whereinthe plurality of openings of the at least one coating stencil isconfigured to apply the adhesive material to only a selected portion ofthe at least one semiconductor component.
 62. The apparatus of claim 59,wherein the plurality of openings of the at least one coating stencil isgenerally rectangular in shape.
 63. The apparatus of claim 59, whereinthe plurality of openings of the at least one coating stencil isgenerally square in shape.
 64. The apparatus of claim 59, wherein theplurality of openings of the at least one coating stencil is positionedgenerally parallel to each other and is spaced so as to have acenterline pitch between each opening of the plurality of openings of0.020 inches (0.051 cm).
 65. The apparatus of claim 59, wherein theplurality of openings of the at least one coating stencil numbers 23 inquantity.
 66. The apparatus of claim 59, wherein the plurality ofopenings of the at least one coating stencil is 0.260 inches (0.660 cm)in length and is 0.010 inches (0.025 cm) in width.
 67. The apparatus ofclaim 59, wherein the plurality of openings of the at least one coatingstencil is sized and configured as a result of considering adhesivematerial viscosity.
 68. The apparatus of claim 67, wherein the pluralityof openings of the at least one coating stencil is sized and configuredto manage a adhesive material viscosity ranging from approximately 1000to 500,000 centipoise.
 69. The apparatus of claim 67, wherein theplurality of openings of the at least one coating stencil is sized andconfigured to optimally accommodate an adhesive material viscosity ofapproximately 62,000 centipoise.
 70. The apparatus of claim 67, whereinthe plurality of openings of the at least one coating stencil is sizedand configured to optimally accommodate an adhesive material viscosityof approximately 62,000 centipoise at a temperature of approximately 77°F. (25° C.).
 71. The apparatus of claim 59, wherein the plurality ofopenings of the at least one coating stencil is arranged generallyparallel to each other and is spaced so as to have a centerline pitchbetween each opening of the plurality of openings of 0.020 inches (0.051cm).
 72. The apparatus of claim 71, wherein the plurality of openings ofthe at least one coating stencil numbers 23 in quantity.
 73. Theapparatus of claim 59, wherein the plurality of openings of the at leastone coating stencil is 0.260 inches (0.660 cm) in length and is 0.010inches (0.025 cm) in width.
 74. The apparatus of claim 59, wherein theat least one first mechanism further comprises a vacuum on a bottom sideof the at least one coating stencil.
 75. The apparatus of claim 53,further comprising at least one third mechanism configured to bring theat least one semiconductor component in contact with the exposed surfaceof adhesive material.
 76. The apparatus of claim 53, wherein theadhesive reservoir further comprises a circulation mechanism configuredto circulate the adhesive material and maintain uniformity of theadhesive material.
 77. The apparatus of claim 53, wherein the at leastone second mechanism is attached to the adhesive reservoir.
 78. Theapparatus of claim 53, wherein the at least one semiconductor componentcomprises at least one lead finger of a lead frame.
 79. An apparatus forapplying adhesive material to one or more underside surfaces of at leastone semiconductor component, comprising: an adhesive reservoir having aplurality of upward facing openings, the adhesive reservoir configuredto provide an exposed surface of an adhesive material contained thereinto each of one or more underside surfaces of at least one semiconductorcomponent positioned thereover and to avoid contacting the exposedsurface of adhesive material with a bond wire surface of each of the atleast one semiconductor components, the adhesive material exhibiting asurface tension; and a pump and control system configured to at leastraise and lower the adhesive material to a desired selectable height andto level the exposed surface of adhesive material at a precise locationabove the at least one upward facing opening.
 80. The apparatus of claim79, wherein the plurality of upward facing openings in combination withthe surface tension of the adhesive material are configured to providethe exposed surface comprising a meniscus.
 81. The apparatus of claim79, further comprising at least one mechanism configured to manipulatethe surface tension of the adhesive material to flatten the exposedsurface of the adhesive material.
 82. The apparatus of claim 79, furthercomprising at least one mechanism configured to manipulate thedifference in pressure within the adhesive material and ambient air tobe equal to twice the surface tension of the adhesive material dividedby a radius of curvature of the adhesive material.
 83. The apparatus ofclaim 79, further comprising at least one mechanism configured to usethe surface tension of the adhesive material to control surface area andthickness of the adhesive material available for application to the atleast one semiconductor component.
 84. The apparatus of claim 79,further comprising at least one of a coating stencil, a wiper, a vacuum,and a height detection mechanism.
 85. The apparatus of claim 79, furthercomprising at least one coating stencil including: a generally planarhorizontal top surface; and a plurality of openings positioned to wetthe at least a portion of the at least one semiconductor component withthe adhesive material, the plurality of openings sized and configured tocontrol extrusion of the adhesive material through the at least onecoating stencil to further increase the exposed surface of the adhesivematerial.
 86. The apparatus of claim 85, wherein the at least onecoating stencil is disposed over at least one upward facing opening ofthe plurality of the upward facing openings, such that the only accessfrom within the at least one upward facing opening to above thereservoir is through the plurality of openings of the at least onecoating stencil.
 87. The apparatus of claim 85, wherein the plurality ofopenings of the at least one coating stencil is configured to apply theadhesive material to only a selected portion of the at least onesemiconductor component.
 88. The apparatus of claim 85, wherein theplurality of openings of the at least one coating stencil is generallyrectangular in shape.
 89. The apparatus of claim 85, wherein theplurality of openings of the at least one coating stencil is generallysquare in shape.
 90. The apparatus of claim 85, wherein the plurality ofopenings of the at least one coating stencil is positioned generallyparallel to each other and is spaced so as to have a centerline pitchbetween each opening of the plurality of openings of 0.020 inches (0.051cm).
 91. The apparatus of claim 90, wherein the plurality of openings ofthe at least one coating stencil numbers 23 in quantity.
 92. Theapparatus of claim 85, wherein the plurality of openings of the at leastone coating stencil is 0.260 inches (0.660 cm) in length and is 0.010inches (0.025 cm) in width.
 93. The apparatus of claim 85, wherein theplurality of openings of the at least one coating stencil is sized andconfigured as a result of considering adhesive material viscosity. 94.The apparatus of claim 85, wherein the plurality of openings of the atleast one coating stencil is sized and configured to manage an adhesivematerial viscosity ranging from approximately 1000 to 500,000centipoise.
 95. The apparatus of claim 85, wherein the plurality ofopenings of the at least one coating stencil is sized and configured tooptimally accommodate an adhesive material viscosity of approximately62,000 centipoise.
 96. The apparatus of claim 85, wherein the pluralityof openings of the at least one coating stencil is sized and configuredto optimally accommodate a adhesive material viscosity of approximately62,000 centipoise at a temperature of approximately 77° F. (25° C.). 97.The apparatus of claim 85, wherein the plurality of openings of the atleast one coating stencil is arranged generally parallel to each otherand is spaced so as to have a centerline pitch between each opening ofthe plurality of openings of 0.020 inches (0.051 cm).
 98. The apparatusof claim 85, wherein the plurality of openings of the at least onecoating stencil numbers 23 in quantity.
 99. The apparatus of claim 85,wherein the plurality of openings of the at least one coating stencil is0.260 inches (0.660 cm) in length and is 0.010 inches (0.025 cm) inwidth.
 100. The apparatus of claim 85, wherein the at least one firstmechanism further comprises a vacuum on a bottom side of the at leastone coating stencil.
 101. The apparatus of claim 79, further comprisingat least one third mechanism configured to bring the at least onesemiconductor component in contact with the exposed surface of adhesivematerial.
 102. The apparatus of claim 79, wherein the reservoir furthercomprises a circulation mechanism configured to circulate the adhesivematerial and maintain uniformity of the adhesive material.
 103. Theapparatus of claim 79, wherein the at least one second mechanism isattached to the reservoir.
 104. The apparatus of claim 79, wherein theat least one semiconductor component comprises at least one lead fingerof a lead frame.